Indirect electron excitation for thermionic vacuum tubes



A. N. LuclAN 1,886,705 INDIRECT ELECTRON EXCITATION FORTHERMIONIC VACUUM TUBES Nov. 8, 1932.

Filed Feb. 6, 1926 lNvENjrQR ARfsENB N. LUCIAN Patented Nov. 8, 1932 ARSENE N. LUCIAN, 0F PHILADELPHIA., PENNSYLVANIA INDIRECT ELECTRON EXCITATION FOR THERMIONIC VACUUM TUBES Application led February 6, 1926. Serial No. 86,387.

This invention relates to vacuum tubes, most particularly to triodes, and to that class of tubes in which the cathode is hollowand forms itself with its own Walls a. part of the vacuous enclosure. The object of the invention is to improve in general the construction of such a tube. More particularly, it is an object of the invention so to construct and coordinate the cathode of such a tube as to improve the excitation thereof for electron emiss1on.

It is an object of the invention to provide for the excitation of such a cathode by the indirect application thereto of heat in an approved manner. It is a further object of the lnvention to localize the temperature rise in such a cathode in response to the applied heat for purposes of excitation. It is a further purpose of the invention, physically, electromagnetically, and electro-statically, to isolate the thermionically functioning circuits of the tube proper from the cathode heating circuit.

The above Will better be understood by reference to the illustrative embodiment of the invention described in the following specification in4 connection with the accompanying drawing, it being understood that such reference is solely for purposes of illustration and not limitation.

In the drawing,

Fig. 1 is a diagrammatic vertical section through a preferred embodiment of my invention; and

Fig. 2 is a fragmentary vertical section illust-rating a modification of the glass to metal seal.

A suitable glass bulb or tube A is provided of the type usually employed to maintain a vacuum therein. the seal-ofi' tip 1 being preferablv located at one side of one end as indicated in the figure. It should be understood that in the drawing illustrated, the tube or bulb A is supposedly a solid of revolution in the form of a hollow shell and completes the usual vacuous chamber B, the degree of vacuum depending upon the desired service for the tube. I contemplate both such a degree that no positive ionization takes place and also such that appreciable ionization is present. It is preferred that a re-entrant portion 2 be provided which carries the lead seal-offA head 3. Within this head are mounted and sealed leads 4, 5, 6, 7, and 8, of which only 4, 6, and 8 are act-ual leads in the figure shown, the remaining ones serving primarily as supports. For example, wires 4 and 7 serve as a support for the plate P, wires 5 and 6 serve as supports for the grid G, and Wires 4, 5, and 8 are respectively the conductor leads for the plate P, grid G and cathode C. In the actual embodiment illustrated, the lead 8 terminates upon the shield C which itself is electrically connected with the cathode C and functionally forms a part of the lead although it serves two other functions in the structure, namely, that of a heat radiator to prevent a high temperature rise at the end 10 of the cathode nearest to the glass seal 11, and also as an electro-static and electro-magnetic shield for the plate and the grid. In the embodiment illustrated, the cathode C is in the form of a hollow tubular thimble, the cylindrical portion 12 of which carries the shield C and also a plurality of fins 13, fabricated in the form of flanged metal discs. the shell C having a driving fit upon the cathode sleeve 12. It should be understood also, of course, that these elements may be attached to the cathode sleeve by welding or the like.

The operative C is preferably formed with a series of circumferential grooves 15 which materially localize the heat within this portion reducing the heat conductivity of the cathode at this locality. The grooves also are preferably filled or partly filled with a coating or filling of electron emitting substance 16. Any of the compounds serviceable for this purpose are contemplated, for example, thorium oxide, calcium oxide, etc. These compounds are of the class which readily emit electrons upon small excitation such as that from heat at a low temperature.

A preferable metal for the fabrication of the cathode C may be employed, it alone being necessary that it be gas-tight, not easily oxidized at the temperature of operation, and possessing a relatively low heat conductivity and a high melting point, there being no need portion 14 of the cathode 80 I to select it with special reference to its ability to make a seal with glass.

This special feature for my cathode construction is rendered possible by reason of the provision of an intermediate iiange or collar D which I interpose between the rim 20 of the tube A and the end 10 of the cathode tube. The metal of this collar D is selected so that it shall have the quality of both sealin to the cathode C and to the glass 11. The co1 ar D is made, preferably, of uniform-thickness throughout, but I may taper either end of it down to a feather edge for purposes of sealing to the metal shell or to the glass.

In Fig. 2, I have illustrated this sealing pit 11 embracing both sides of the edge 21, while in Fig. 1, I have shown it formed substantially upon but one side or surface of this edge. The sealing of the collar D to the cathode C may be effected by welding or hard soldering 22.

I call particular attention to the fact that the leads 4, 6, and 8, serving the purposes of causing and controlling electron emission within the tube, emerge exclusively from one end of the structure while the hollow cathode C is thermially and externally reach able from the opposite end of the tube A. For example, a removable heater E together with its heating circuit leads and 26 emerge from the said opposite end of the tube structure.

In the embodiment illustrated, the heater E comprises a stem 27 of insulating material perforated to accommodate the leads 25 and 26. A hairpin shaped heater element 28 occupies the hollow chamber 29 within the wall 14 underlying the grooves 15 and is formed of any suitable electrical resistance metal, while leads 25 and 26 are preferably copper. The lead 25 terminates in a copper collar 30 mechanically held by the boss 31. It is to be understood that any preferred type of socket mount may be provided for both ends of the tube A and to accommodate the electric leads and further that the fit of the stem E within the cathode C is suciently loose to accommodate the expansion and contraction for changed temperature conditions of the air within chamber 29. Also, the exact positioning of the stem E and its carried parts within the cathode may be effected by any suitable form of mounting, it being merely the purpose in this application to illustrate and describe specifically the elements and their relations which have actually so been described. It is further to be understood that the electrode construction shown for this tube are by no means limited for use with the specific form of heater E illustrated and described, and it is still further to be understood that the cathode construction illustrated is by no means limited in its embodiment to all of the features illustrated herein. For example, it is fully contemplated that the shield C and the heat radiators 13 useful to impose a potential drop along the cathode and may or may not be used.

The inventive thought may have a variety yof expressions as is contemplated in what I claim and desire to secure by United States Patent as follows:

1. In a thermionic device in combination, a glass envelope; a plurality of electrodes cooperatively positioned and mounted within said envelope and including a cathode; a plurality of lead-in wires one for each of said electrodes, all emerging from one end of said tube; a heater for said cathode removable from the other end of said tube; and heating circuit leads for said removable heater emerging from the same end of said tube from which the heater is removable.

2. In a thermionic device, an anode; a hollow metal cathode, the walls of said cathode forming a continuous part of the vacuous enclosure: and a combined shield and heatradiating means connected to and surrounding said cathode said shield extending to enclose the cathode at its active part to provide an electromagnetic and electrostatic shield therefor.

3. In an audion construction, an envelope, a hollow cathode in said envelope and sealed thereto so as to open exteriorly thereof, said cathode having a corrugated surface on its inner face coated with a thermionically active material and a heater element adapted to be removably supported within said hollow cathode.

4. In a thermionic tube, a vacuous glass chamber. a' hollow cathode having an electron emitting surface within the vacuous chamber, said cathode and chamber being sealed together with the interior of the cathode open to the outside of the chamber, a removable electric heater for said cathode located within the hollow cathode, a magnetic shield between said heater and the inside surface of the cathode constructed to permit removal of the heater, and a radiating shieldl secured to thehollow cathode to act as a radiator of heat to prevent weakening of the seal between the cathode and the chamber.

5. In a thermionic tube, an envelope, a hollow cathode sealed to said envelope to open exteriorly thereof.I andY heat radiating means supported on said cathode between the seal and the portion to be heated and within the envelope to prevent weakening of the seal.

6. In a thermionic tube, an envelope, a

hollow cathode sealed to said envelope to open exteriorly thereof, a. thermionic coating on the surface of the cathode and a removable heater fitting Within the cathode, said cathode being of materially reduced thickness below the portion to be heated and between it and the seal to restrict the iiow of heat vthereby to prevent weakening of the seal. f

7. In a thermionic device, a vacuous envelope and a hollow cathode sealed thereto and opening exteriorly `of the envelope, the surface of the cathode exposed to the interior of the envelope being corrugated to localize the heat at this portion thereof.

f 8. In a thermionic tube, an envelope, a hollw cathode sealed to said envelope and opening exteriorly thereof, a thermionic coating. for said cathode, a removable heater fitting within said hollow cathode and an electromagnetic and electrostatic shield between the heaterand the cathode, said shield being completely closed at one end.

9. In a thermionic tube, a vacuum tube, the combination comprising an envelope, a hollow cathode, a grid and plat/eJ surrounding said cathode and lying within said envelope, a heater element for said cathode, an electromagnetic and electro-static shield within the cathode enclosing said heater and a second electro-magnetic and electro-static shield encircling all of the electrodes.

. 10. In a thermionic device an envelope and a hollow cathode, the surface of the cathode being corrugated, and a heater element for said cathode.

ARSENE N. LUCIAN. 

